F-35 Weapons Tests in 2014 Focus On Amraam

With weapons testing becoming a more regular event for the F-35 program, developers are looking ahead to a fast pace of trials this year to prepare for the first operational use of the stealthy, single-engine fighter by the U.S. Marine Corps in 2015.

Delivering weapons is often described as the “business end” of a fighter's job, and the Marines are planning to declare initial operational capability (IOC) for the F-35B using the aircraft's 2B software release as early as July 2015, and no later than December 2015, the service hopes. Though limited to use of three weapons—the 1,000-lb. GBU-32 Joint Direct Attack Munition (JDAM), GBU-12 500-lb. Laser-Guided Bomb and Advanced Medium-Range Air-to-Air Missile (Amraam) AIM-120 series—the F-35B will surpass the current capability of the AV-8B Harrier jump jet and F/A-18C twin-engine Hornets, says Lt. Gen. Robert Schmidle, commandant for Marine Corps aviation.

The F-35 Joint Program Office plans to complete its weapons flight testing for use of these systems and the 2B software by March of 2015 to accommodate the service's IOC aspirations, says Charlie Wagner, weapons team lead for the program.

The U.S. Air Force is planning to follow quickly with an IOC declaration as early as August 2016 and no later than December of that year with its F-35A, using the 3I software release, which includes the limited 2B weapons capability, new processing hardware and the addition of the 2,000-lb. GBU-31 JDAM that shares the same software as its smaller, 1,000-lb. cousin. The U.S. Navy will follow later with an IOC between August 2018-February 2019. All nine partner nations—and three other confirmed buyers—are eager to ramp up weapons testing for the aircraft.

Roughly 11 shots remain to be tested with the limited 2B software package, Wagner says. The 3F flight-test campaign for weapons will be far more extensive, with more than 30 guided launches now planned. The 3F software is aligned with far more weapons, including: the 250-lb. Small-Diameter Bomb (SDB) I GBU-39; AGM-154 Joint Standoff Weapon; 2,000-lb. JDAM employing the BLU-109 penetrator warhead; a general purpose 2,000-lb. Mk. 84 bomb; the Paveway IV laser-guided bomb; and AIM-132 Advanced Short-Range Air-to-Air Missile (both for the U.K.), as well as the use of external stores.

By the end of last year, developers had conducted guided tests of all three weapons for the USMC IOC, the last of which was a guided flight for the GBU-32, a trial that suffices for Marine Corps, as both JDAMs use the same software, Wagner says.

The most challenging testing, however, is yet to come, as overseers will run the F-35 and the Amraam against increasingly complicated threats. “Every shot we take is getting more and more complex,” Wagner says. The Amraam's mission to destroy airborne threats is the most challenging of the three USMC IOC weapons, and the weapon's flight profile in a chase can create highly stressing conditions for its data link to communicate with the F-35 for targeting updates.

Now that safe separation and motor firing have been demonstrated, the team is focusing on accuracy. Eventually, the F-35 and Amraam will be pitted against increasingly complex electronic countermeasures (ECM) to verify that they are effective in realistic threat environments.

The F-35, which employs an unprecedented suite of electro-optical and infrared sensors as well as a premier active, electronically scanned array (AESA), is equipped to maximize the use of the Amraam, especially the forthcoming D model, which features an improved data link and upgraded capabilities in a heavy ECM environment.

Wagner says the team will test with a variety of Amraam models, including the C3, C5 and C7, which has upgraded electronics cards. The full capability of the D will be reached with the Block IV F-35 weapons release. “We are talking to it like it is a C7,” Wagner says of the new D, which remains in protracted development as Raytheon sorts through technical challenges.

The Block IV capability is slated to be operational in 2020-22, Wagner says. The majority of the remaining launches in the 2B test campaign will expand the use of Amraam and experiment with its various modes of employment.

Although with the bay doors open, the F-35 generates vibration levels exceeding those against which the Amraam has been tested, “right now I don't have any indication this is an aircraft problem,” Wagner says. “Because the bay doors are open for only a very limited amount of time, . . . that short duration is significant, but it is not something that I am too worried about.”

Close-in weapons, such as the AIM 9X Sidewinder and the gun (externally mounted for the Marine Corps and internally mounted for the Air Force), will require the expanded capability and flight envelope of the 3F software package used on the aircraft.

Also included in the 3F package will be the more exotic non-kinetic effects the AESA can have on targets, such as electronic attack. “We start turning the systems on in 2B, but they get matured and refined as we go into 3F,” Wagner says.

Along with a hearty set of weapons tests in 2014, the F-35 program also will emphasize preparations for F-35C aircraft carrier trials.

Engineers are continuing to refine data on potential thermal issues in the weapons bay as it carries ordnance. “The data that we have gotten so far show that the bay can get hot,” Wagner says. “But it is only in specific parts of the flight envelope on specific days where we start seeing temperatures that are high enough that cause us concern.”

He notes that the team is incorporating lessons from the storage and use of weapons in Afghanistan and Iraq, both extreme heat environments, including how hot weapons can be before they are loaded into the bay and called upon during a mission.

Wagner says the thermal and vibration analysis should be complete in the next 15 months, in line with wrapping up testing for the USMC IOC.

The use of the so-called Gen 2 F-35 helmet, which lacks a new night camera function and anti-jitter equipment planned for the Gen 3 upgrade, is not a limiting factor for testing weapons for the 2B release, Wagner says. The integrated helmet-mounted display with the more advanced features will, however, be needed if the F-35 is called upon for close-in fights that require pilots to use Amraam or AIM 9X missiles against targets at extremely high off-boresight angles.

Though not part of the USMC or USAF IOC plans, developers have begun fit tests of the GBU-39 SDB. At 250 lb., it is designed to allow for the use of a four-pack in place of each store sized for a 2,000-lb. GBU-32 JDAM, maximizing the number of ground targets a single F-35 can attack. Wagner says that during fit and pit tests, the only issue has been a need to move some wiring bundles for safe operation.

Meanwhile, the F-35 test program is looking to trim cost where possible. As the top aviation procurement priority for the Defense Department, it has been largely shielded from the cuts gutting other aircraft projects. But the pressure is on to reduce the costs estimated at nearly $400 billion to develop and field the aircraft. Wagner says the weapons team is looking to execute as many drops as possible in a single sortie to save some money. Typically, weapons tests include one drop for one sortie, but Wagner estimates as much as $250,000 can be saved by eliminating a single flight. The team managed to drop two weapons in a recent, single test flight, he says.

Discuss this Article 1

Watching video of the GBU-12 exiting the bay in the first guided release, I was struck by both the momentum and the late period pitch instability of the release.

Given it is dropped toed in, one would expect some separation anomalies as sideforce yaw events but the weapon was instead showing some pretty serious see-saw deviations which could have effected birdie alignment and gimbal stress on a weapon which is naturally not going to be locked on at release (and PII doesn't have an IMU...)

I don't know if the jet has bay spoilers but I wonder what the flow field off the nose really is really harsh enough to induce that kind of wobble or if it is related to some kind of guidance pickup CCG struggling with the smaller canards of the PII weapon trying to stabilize force moments.

Early Paveways had the option of plug-in outer panels which made fin span greater but this is no longer the case on external carriage PII weapons.

It may be something to consider in either a GBU-22/Paveway IV configured munition.

Of course, the GBU-12 is a long weapon for it's weight class but this what begs trouble is in fact the GBU-39/53 which both are much shorter weapon with much smaller tail controls.

If there is a boundary flow field effect on the GBU-12, it is possible that it will be much worse, depending on fore/aft station positioning, for the SDBs as they have to execute the rollover on wakeup. This could be magnified by their overall lower mass and short control displacement arm, depending on how much thrust force is required to push the weapon through the bay boundary at a given station.

As for the AIM-120... The APG-81 has maybe 2/3rds the AESA modules that the APG-77 does and that will definitely effect maximum acquisition and tracking range. In combination with the jet's -4/-15/-43 second acceleration lag this will likely rob the pilots of the missile's outer envelope, particularly if you are playing shooter:illuminator (chainsaw/pump/pincer) games with a second section in trail or offset to maximize standoff on MCG lightup.

If so, we need to consider how much VLO can truly offset lower -missile- aerodynamic performance overall as a function of acquiring alternative weapons like the CUDA with which to increase bay counts.

If you can (only, reliably,) fire within 15nm regardless, there is no need to go for an AIM-120D.

Since a followon to AMRAAM is not even in the cards (despite the F-22 community having yelled for more shots, since 2006) it looks to me as though the airframe is factually not going to be a functionally complete weapons system from the get go.

Nor can you compensate with numbers because the typical Marine detachment strength to a boat is on the order of 6-8 airframes which is barely enough to stage a FORCAP.

In relation to this, I am reminded of the bad ol' days when F-4C/D/E in Vietnam would fly dozens of missions with the AIM-7s uploaded as though a wooden round, launch them and 'Suhpraz! Suhpraz!', find they had failed. While this was complicated by other factors ('vibration' from unsprung load trailers, lack of diagnostics gear and adequately trained technicians) the notion that a vibration issue is not critical to range tests where the round is not carried for mission after mission with other ordnance expending while it is conserved is specious.

In war, real air combat occurs maybe 10% of the time but you still have to fly the airframe equipped as though it was going to happen the very next mission.

What then occurs is a divergent variation between carriage hours and TBO depot requirements. If the F-35's carriage environment is harsh on an aero acoustic level -once-, then imagine what it will be like being stuck on a launcher for sortie after sortie as the doors both open and only the A2G munition is released. Until the moment when the AMRAAM is needed. And fails.

As the Specwar are famous for saying: "One is none and Two is one." (If one breaks you have nothing left but harsh language, if you have two and one breaks with three enemy, you're still in trouble...).

Except in this case there is literally no room for the corollary: "When in doubt, load it out." because the LAU-142 or similar rail for an AAM is almost certainly going to be different than the BRU for an IAM.

Having to switch around AMRAAMs between missions to keep total accumulated cycle times low will be a pain for turn rates in a surge-expeditionary sortie generation scenario and likely depot expensive if the weapon is seriously exceeding it's rated Hertz threshold or temperatures as well.

An interim fix would be to qualify the tip station AAMs and simply 'not talk about' the AMRAAM you don't load for most SSC/LIC missions.

I don't know what the ultimate solution is here. If we write a spec tomorrow, we are still likely 5-10 years away from having a reliable standin for AMRAAM and the only alternative, the EWP, is not being considered for the F-35 in public literature.

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